1-(4-fluoro-phenyl)-4-((6bR,10aS)-3-methyl-2,3,6b,9,10,10a-hexahydro-1H,7H-pyrido[3′,4′:4,5]pyrrolo[1,2,3-de]quinoxalin-8-yl)-butan-1-one (sometimes referred to as 4-((6bR,10aS)-3-methyl-2,3,6b,9,10,10a-hexahydro-1H-pyrido[3′,4′:4,5]pyrrolo[1,2,3-de]quinoxalin-8(7H)-yl)-1-(4-fluorophenyl)-1-butanone, or as ITI-007), has the following structure:

ITI-007 is a potent 5-HT2A receptor ligand (Ki=0.5 nM) with strong affinity for dopamine (DA) D2 receptors (Ki=32 nM) and the serotonin transporter (SERT) (Ki=62 nM) but negligible binding to receptors (e.g., H1 histaminergic, 5-HT2C, and muscarinic) associated with cognitive and metabolic side effects of antipsychotic drugs. ITI-007 is currently in clinical trials, i.a., for treatment of schizophrenia. While ITI-007 is a promising drug, its production and formulation present challenges. In free base form, ITI-007 is an oily, sticky solid, with poor solubility, not only in water but also in many organic solvents. Making salts of the compound has proven to be unusually difficult. A hydrochloride salt form of ITI-007 was disclosed in U.S. Pat. No. 7,183,282, but this salt is hygroscopic and shows poor stability. A toluenesulfonic acid addition salt (tosylate) of ITI-007 was finally identified and described in WO 2009/114181.
There is a need for alternative stable and pharmaceutically acceptable salts and polymorphs of ITI-007.